Rotor blade for rotative winged aircraft



July 26, 1949. H. s. CAMPBELL 2,477,113

ROTOR BLADE FOR ROTATIVE WINGED AIRCRAFT Fuga Feb. 19, 1942 2 sheets-sheet 1 MMMNTOR July 26, 1949. H. s. CAMPBELL ROTOR BLADE FOR ROTATIVE WINGED AIRCRAFT 2 Sheets-Sheet 2 Filed Feb. 19, 1942 Psanaulizs, I1949 UNITED STATES no'ron BLADE PATENT oFFlcE FOR ROTATIV E WINGED AIRCRAFT Application February 19, 1942, serial No. 431,460

l This invention relates to rotor vblades for use in rotative winged aircraft.

In aircraft sustaining rotors, the blades are commonly plvotally connected to a rotative hub, each blade being of considerable length as compared with its chord dimension, for instance twelve to fifteen times. In accordance with present practice, it has been common to construct the blades in a manner incorporating a longitudinal strength structure or spar extended substantially throughout the entire length ofthe blade, together with .blade contour defining means built up on said spar.

In accordance with the present invention, the blade is at least in major part composed of a stressed skin serving not only as the longitudinal strength structure, but also as the contour delining means. This is achieved in accordance with the invention by the employment of molded sheet material, for instance plywood, the sheet material being shaped over forms or the like, as

is explained more fully hereinafter.

To carry the centrifugal load during rotation of the blade, a mounting means is provided toward the root end thereof, the mounting means being secured at a multiplicity of points distributed over an extended area of the stressed skin.

In accordance with the foregoing, blades may be constructed of less expensive materials and with very much less work than has been customary heretofore.

Another feature of the invention is the provision in the molded sheet material stressed skin blade above mentioned of a longitudinal bulkhead or strengthening rib interconnecting the upper and lower sides of the blade intermediate the nose and trailing edges, this rib desirably being molded integrally with at least the nose portion of the blade.

In the'preferred arrangement, the nose portion of the blade, including the rib just mentioned, const itutes a box section, desirably of 'greater wall thickness than the trailing edge portion of the blade. This has the advantage `of maintaining the sectional center of gravity of 'the blade well forward. In addition, I contemblade to ,thisv box nose section, so that the centrifugal load during operation is most effectively transmitted from all parts of the blade to the boxv section, and thence inwardly to the root end mounting and to the hub.

How the foregoing and other objects and ad- 1 Claim. (Cl. 170--159) 2 i the following description, referring to the accompanying drawings, in which- .Figure 1 is a plan outline view of a blade constructed in accordance with this invention;

Figure 2 is a fragmentary plan view on an enlarged scale of the inboard end portion of the blade, particularly illustrating the attachment of the root end mounting means; l

Figures 3 and 4 are enlarged sectional views taken as indicated by the lines 3 3 and 4 4, respectively, on Figure 1;

Figure 5 is a sectional view of a modified blade structure, the view also showing certain parts employed in fabrication of the blade;

Figure 6 is a sectional view through a portion of the blade of Figure 5, together with certain blocks or. mold parts adapted tobe used in the manufacture of the blade: and

Figures 7 and 8 are sectional views taken, respectively, on the lines 1 1 and 8 8 of Figure 6.

As seen in Figure 1, the blade is of considerably elongated plan form and is preferably tapered toward the tip. At the inner end of the blade a mounting structure 9, having an apertured lug, may serve for pivotal attachment of the blade to a rotor hub. Preferably, the attachment includes at least a "apping pivot providing freedom for swinging movement of the blade in a direction generally transverse its mean rotative path of travel.

As seen in Figure 3, the nose portion l0 of the blade is formed of several wood plies (three being indicated in the drawing), there being a 35 rib or bulkhead Il closing the rear end of the nose box and serving to interbrace the upper and lower sides of the blade. The trailing edge portion of the blade. indicated at I2, is shown as of substantially less thickness than the nose 40 part. It is contemplated that both the trailing edge portion Il and the nose portion Ill shall be integrally molded of plywood or other moldable sheet material, the several plies being worked together and joined at the junction points, forinstance at rib -l I, in a manner now well understood in the molding of plied articles.

Although onlya single ply is indicated in the trailing edge portion Il of. the blade, it is to be understood that several plies may here be used,

as in the nose `portion, although by preference thenumber of plies in the nose portion would be considerably greater than in the trailing edge portion, with a view to vaffording greater wall thickness, strength and weight in the nose. The

vantages are attained will appear more fully from plies may be cemented or glued together or im- 3 pregnated with plastic adhesive material' in accordance with known practice. Grdinarily, heat would be employed in the shaping and molding of the plies for the purposes of the present invention.

Toward the outboard end of the blade (to the right in Figure 1) the wall thickness of the nose box is preferably tapered or reduced in steps, as is indicated at Illa in Figure 4, the tip portion not requiringthe strength of the inboard portion and desirably being of lighter weight. The trailing edge portion I2a toward the outboard end of the blade may also be reduced in thickness. Some reduction in thickness in rib l I is also contemplated in the outboard region. The reduction in thickness toward the tip may be brought about either by decreasing the number of pliesl employed or by decreasing the thickness of the individual plies.

When viewed in plan, the location of rib Il (as clearly appears in Figure 1) is such that the chamber formed in front of said rib, as well as -the chamber formed to the rear of said rib, is tapered. This taper, coupled with the taper in thickness, which will be apparent from comparison of Figures 3 and 4, permits forming the blade by shaping the plies around elongated mold pieces, which pieces, following the molding, may be withdrawn inwardly, i.' e., from the inboard end of e the blade.

.The blade mounting means may effectively be composed of a built up box comprising upper and lower plates i3 and Il and a pair of vertical flanged members l5 and I6 secured together and fastened to the nose box of the blade by means of rivets I 1. Examination of Figure 2 shows that therel are a multiplicity ci vthese rivets il distributed in series over an extended length of the blade. Additional series of rivets I8 serve to further attach the plates I3 and il to the upper and lower sides of the nose box of the blade.

From the foregoing it will be seen that the molded sheet material constitutes a stressed skin serving not only as the strength structure of the blade but also as the blade contour dening means. If desired, fabric may be doped over the outside surfaces.

In the form of construction illustrated in Figures 5 to 8 inclusive, the blade again incorporates a box section defining the nose portion of the blade as indicated at Ia. As before, a multiplicity of plies are incorporated in the nose section. Although the root end mounting for the blade is not illustrated in Figure 5, it will be understood that this mounting may be applied in the same manner as shown in Figure 3.

The primary difference between the construction of Figures 5 to 8 and that of Figures 1 t0 4 Y is that in Figures 5 to 8, the trailing edge portion of the blade is built up separately from the nose portion, instead of in the unitary manner of Figures 1 to 4. Thus, the blade of Figures 5 to 8 inclusive is built up in two parts (nose part and trailing edge part) and then the two parts are secured together in the manner illustrated in Figure 5. Before full discussion of Figure 5, however, reference' is made to Figures 6, I and 8 which illustrate the manner in which the trailing edge portion of the blade is built up.

The trailing edge section of the blade coni-V prises sheet material IS defining the contour of the trailing edge part, which sheet material desirably, though not necessarily, is also of molded ply construction. The sheet material I8 is secured to and braced by a series of partial ribs 2li, each of which may be apertured as indicated for lightness. A trailing edge stringer 2i may be located inside the sheet material along the trailing edge.

Forthe purpose oi.' .molding the .trailing edge section oi the blade, the sheet or ply material I! may be bent over a wedge shaped block 24 which is slotted inwardly from the rear edge to provide separated parts 22, between which ribs 20 are received. This construction appears in Figure 8, and from Figure '1 it will be seen that the forward portion of block 24 is grooved to receive the forwardly projecting end portions of the ribs 20. The assembly (including sheet material I8, ribs 20. trailing edge Stringer 2i and the block 2l) may be inserted into an appropriately shaped cavity in a block 23, for the purpose of shaping the sheet ma tterial I9 and molding the same to the desired conur. l

Having formed a nose box and also a trailing edge portion in the manner described just above, these two parts of the blade are brought together as indicated in Figure 5, and pressure is applied by means of members 25-25, so as to secure the trailing edge portion to the nose box. For this purpose an appropriate adhesive or moldable material is applied to the interntting surfaces between the nose box and the trailing edge portion.

As before, lf desired, the exterior surfaces of the blade of Figures 5 to 8 may be nnished merely by painting, although it is also contemplated that fabric may be applied and doped onto the blade.

For strengthening and ballasting, the strip or Stringer 26 may be located just inside the nose of the blade, this feature being applicable to either form of construction described.

In both forms of construction described, at least a large part of the airfoil contour of the blade section is defined by a stressed skin, which skin further serves as the primary strength structure of the blade.

According to the invention, the type of construction herein contemplated, especially the employment of moldable sheet material, is effectively adapted to fabrication of sustaining rotor blades. The construction is inexpensive and simple, while at the same time of considerable strength and reasonable lilexibility, which latter is of importance in accomr xodating normal flexing and deformation of the blade which occur in operation.

I claim:

A rotor blade adapted for mounting on an air craft rotor hub and having a length many times its chord, said blade comprising a self-bracing tubular structure formed of laminated sheet material molded to provide a stressed skin having an external surface which serves to define airioil contour throughout at least the leading edge portion of the blade; attachment means mounting said blade on a rotor hub, said means comprising a stub spar-projecting into said tubular structure intermediate the front and rear edges thereof, and being secured to the upper-and lower surfaces of said laminated stressed skin by a number of fastenings uniting said spar and said stressed skin at a plurality of spaced points; said tubular structure further having a longitudinal rib integrally united with the upper and lower parts ot said laminated stressed skin, and spaced appreciably to the rear of said stub spar; a 'trailing portion of said blade being formed of upper and lower material sheets, the forward edges of which are bonded to laminations ofthe upper and lower parts of the stressed skin adjacent the upper and lower edges of said rib, said structure further being characterized in that the tubular structure in advance of the longitudinal rib is o! substantially uniform wall thickness throughout. and is of greater wall thickness than the tubular structure lying to the rear of said longitudinal rib.

HARRIS S. CAMPBELL.

REFERENCES CITED The following references are of record 'in theille of this patent: f

Number Number Name Date Klemm July 12, 1938 Bennett Dec. 12, 1939 Clark Oct. 7, 1941 Darnier Oct. 14, 1941 Allward Feb. 24, 1942 Pullin Dec. 1, 1942 Vidal Dec. 14, 1943 Pecker Nov. 7, 1944 Berliner Feb. 27, 1945 FOREIGN PATENTS Country Date l Great Britain Dec. 13, 1937 France Apr. 30, 1927 Germany Dec. 18, 1940 

